1. Field of the Invention
This invention relates to a method of manufacturing a contact lens, and, in particular, to a method of manufacturing a contact lens from two or more differing materials, for example a composite lens, bifocal or trifocal lens.
2. State of the Art
Normally contact lenses when formed from two or more materials are formed with a first member formed from a first material, and a second member formed from a second material. One particular example of this is a composite lens which is generically known as "Saturn" in the industry wherein the first member comprises the optical zone of the lenses and is normally made from a "hard" material such as a rigid gas permeable (RGP) material, and the second member comprises a skirt around the optical zone and is normally made from a "soft" material, such as a hydrogel material. At present composite lenses of the general type described above are manufactured from buttons that are formed by the following process steps:
forming a first rod of material by polymerisation of a first monomer material; PA1 forming a layer of a second material about said first rod of material by polymerisation and PA1 transversely slicing the rod so formed into buttons. PA1 the fact that the first rod of material must be located centrally within the finished buttons. With the procedures employed in the industry this is not so easily achieved, and consequently there is considerable scope for error from this aspect, leading to a high rejection level of rods and buttons; PA1 the actual diameter of the first rod of material provides the dimensions of a significant characteristic of the finished lens. Therefore the first rod of material has to have a uniform diameter; and PA1 the adhesion between the two materials of the two members as a result of the different character of the materials of the composite lens may be very low, and when this is combined with the fact that the soft contact lens material will be swollen after manufacture and prior to use exerting a considerable force on this adhesion the problems can be significant. PA1 casting a first monomer material into the receptive well of the casting mold, and polymerising/curing the monomer material; and PA1 machining the article formed by the above casting into a contact lens PA1 wherein the first monomer material includes a polymerisable material which has a penetrating like action with respect to the material from which the end wall of the casting mould is formed. PA1 casting a first monomer material into one of the receptive wells of the casting mould, and polymerising/curing the monomer material; PA1 casting a second monomer material into the other receptive well of the casting mould, and, polymerising/curing the monomer material; and PA1 machining the article formed by the above castings into a contact lens PA1 one receptive well which is defined by the inward displacement in the end wall of the casting mould only; and PA1 one receptive well which is defined by the side wall and the end wall.
The problems associated with the above mentioned manufacturing technique for the button include:
The net result of the above is that the production of composite contact lens using buttons in accordance with the above detailed method is expensive, with a high rejection of rods, buttons and lens.
Above the situations and problems have been discussed with regard to one particular example, namely a "Saturn" lens, it should however be noted that the situation and problems ape very similar to those that would be encountered for the production of bifocal and other multifocal lenses from two of mope different polymeric materials.